An important factor for the correct operation of most refrigeration compressors is the adequate lubrication of the components which have a relative movement between each other.
The lubrication is obtained by pumping lubricant oil provided in an oil reservoir defined in the interior of a lower portion of a generally hermetic shell. This oil is pumped until reaching the parts of the compressor presenting relative movement, wherefrom said oil returns to the oil reservoir.
In compressors of the reciprocating type, the vertical crankshaft carries a lubricant oil pump, which conducts said oil to the compressor parts to be lubricated, using the rotation of said crankshaft. In these constructions, the oil is pumped from the oil reservoir by spinning and mechanical dragging.
The most employed concept for oil pumping in compressors is based on the centrifugal effect to carry out the pumping. The centrifugal effect uses the pump rotation speed to generate a centrifugal force in the oil, as described in the patent documents WO93/22557, U.S. Pat. No. 4,478,559, U.S. Pat. No. 4,569,639, U.S. Pat. No. 4,097,185, FR2492471 and JP60-069275.
In these constructions, the oil pump generally presents a pump body and a shaft, one of said parts of pump body and shaft being rotatively stationary in relation to the other part, so as to allow a dragging effect on the oil being suctioned by centrifugal force, resulting from the rotation of the motor, one of said parts being also provided with helical superficial channels, in which the oil is ascendingly dragged.
The solution WO93/22557 presents the pump shaft, externally provided with helical grooves, affixed to the crankshaft, in order to rotate therewith, a tubular sleeve being attached to the electric motor stator by a fixation rod, said tubular sleeve being mounted around the pump shaft with a radial gap.
The solution U.S. Pat. No. 6,450,785 presents the pump shaft externally provided with helical grooves on its outer surface and interiorly attached to the electric motor stator, in order to remain stationary, while the tubular sleeve rotates together with the shaft and the rotor of the electric motor.
The solution object of Brazilian Patent Application PI0604908-7 presents an oil pump in which the tubular sleeve is provided with helical grooves on its inner surface and affixed to the rotor-crankshaft assembly, the pump shaft being attached to one of the parts of stator and shell.
In the document U.S. Pat. No. 4,097,185, the crankshaft interiorly carries a pump shaft comprising only a tubular body provided, in its interior, with an inner impeller blade. This construction presents, as advantages in relation to the other known constructions, a manufacturing economy and a lower tendency to failure. However, such construction requires a higher precision in mounting the impeller blade in the interior of the pump body, also favoring the occurrence of failures.
Another known solution is described in the Japanese patent document JP60-069275 related to an oil pump comprising a tubular body interiorly closed by a flat wall in which are eccentrically provided windows which are cutout, so as to define respective fins which are displaced, by thermal variation of the lubricant oil, between an inoperative position, substantially coplanar to their rotation plane with the pump body, and an operative position, substantially transversal to said rotation plane, to operate as fins acting on the oil mass, directing it inwardly to the pump body through the cutout windows and forcing it ascendingly, by spinning, along the inner wall of the pump body.
Although defining one or more windows which capture oil in the lower end of the pump body, this previous Japanese solution places these cutout windows in a condition in which they do not produce, by themselves, suction of the oil to the interior of the pump body upon the rotation of the latter, requiring the provision of the fins as deflecting elements to direct the oil through said windows. This solution presents a constructive sophistication which raises considerably the production cost of said component. Moreover, the oil admitted in the interior of the pump body is ascendingly pumped, by spinning, requiring the pump body to present an inner construction which produces the ascending pumping force, from the centrifugal force applied to the oil mass by the fins.